CONDUCTION AND KADIATION 91 



12. Why is loosely woven clothing warmer in winter than more closely 

 woven fabrics? 



13. Why may loosely woven clothing be cooler in summer than more 

 closely woven fabrics? 



14. Which is warmer, close-fitting or loose-fitting underwear? Why? 



15. How do double windows keep the house warm in winter? 



16. Do we warm our clothes, or do our clothes warm us? 



17. Ice-houses and refrigerators have double walls between which is 

 a packing of sawdust, charcoal, cork-dust, or the like. How does this 

 help to keep the ice from melting? 



18. Wrapping the ice in the refrigerator with newspaper will retard 

 the melting of the ice. How does this affect the temperature of the 

 refrigerator? 



19. Ordinary electric light bulbs have no air in them. Certain others 

 are filled with nitrogen gas. Why do the bulbs of the latter get so much 

 hotter? 



20. Why does a crack in the outside of a thermos bottle impair its 

 usefulness? 



21. Snow is called "the poor man's manure" because it protects the 

 crops left out over winter from sudden changes of temperature. How 

 does it do this? 



22. The outer bark of trees consists of many dead cells containing air. 

 How does this protect the trees from sudden changes in temperature? 



